A typical alternating-current surface discharge type panel used as a plasma display panel (hereinafter referred to as “panel”) has many discharge cells between a front plate and a back plate that are faced to each other. The front plate has the following elements:                a plurality of display electrode pairs disposed in parallel on a front glass substrate; and        a dielectric layer and a protective layer for covering the display electrode pairs.Here, each display electrode pair is formed of a pair of scan electrode and sustain electrode. The back plate has the following elements:        a plurality of data electrodes disposed in parallel on a back glass substrate;        a dielectric layer for covering the data electrodes;        a plurality of barrier ribs disposed on the dielectric layer in parallel with the data electrodes; and        phosphor layers disposed on the surface of the dielectric layer and on side surfaces of the barrier ribs.The front plate and back plate are faced to each other so that the display electrode pairs and the data electrodes three-dimensionally intersect, and are sealed. Discharge gas containing xenon with a partial pressure of 5%, for example, is filled into a discharge space in the sealed product. Discharge cells are disposed in intersecting parts of the display electrode pairs and the data electrodes. In the panel having this structure, ultraviolet rays are emitted by gas discharge in each discharge cell. The ultraviolet rays excite respective phosphors of red (R), green (G), and blue (B) to emit light, and thus provide color display.        
A subfield method is generally used as a method of driving the panel. In this method, one field is divided into a plurality of subfields, and the subfields at which light is emitted are combined, thereby performing gradation display.
Each subfield has an initializing period, an address period, and a sustain period. In the initializing period, initializing discharge is caused, a wall charge required for a subsequent address operation is formed on each electrode, and a priming particle (an excitation particle for causing address discharge) for stably causing address discharge is generated.
In the address period, address pulse voltage is selectively applied to a discharge cell where display is to be performed to cause address discharge, thereby forming a wall charge (hereinafter, this operation is referred to as “address”). In the sustain period, sustain pulse voltage is alternately applied to the display electrode pairs formed of the scan electrodes and the sustain electrodes, sustain discharge is caused in the discharge cell having undergone address discharge, and a phosphor layer of the corresponding discharge cell is light-emitted, thereby displaying an image.
In this subfield method, the following operations are performed. In the initializing period of one of a plurality of subfields, the all-cell initializing operation of causing discharge in all discharge cells is performed. In the initializing period of other subfields, the selection initializing operation of selectively causing initializing discharge in the discharge cell having undergone sustain discharge is performed. Thus, light emission that is not related to the gradation display is minimized, and the contrast ratio can be improved.
As a circuit for applying a sustain pulse to a display electrode pair, the so-called electric power recovering circuit capable of reducing power consumption is generally used (e.g. patent document 1). Patent document 1 discloses an electric power recovering circuit, focusing attention on a fact that each display electrode pair is a capacitive load having an inter-electrode capacity of the display electrode pair. The disclosed electric power recovering circuit LC(inductance-capacitance)-resonates an inductor and the inter-electrode capacity using a resonance circuit including the inductor as a component, recovers the electric power stored in the inter-electrode capacity in a capacitor for electric power recovery, and recycles the recovered electric power for driving the display electrode pair.
Recently, the screen size and definition of the panel have been further increased, and hence various studies of improving the luminous efficiency of the panel and improving the luminance have been performed. For example, a study of largely increasing the luminous efficiency by increasing the xenon partial pressure has been performed. When the xenon partial pressure is increased, however, variation in timing of causing discharge increases, the light emission intensity in each discharge cell varies, and the display luminance can become un-uniform. In order to improve the un-uniformity of the luminance, a driving method is disclosed in which the rising period is shortened once per a plurality of times in the sustain period, for example, a sustain pulse whose rising is steep is inserted, the timing of the sustain discharge is aligned, and the display luminance is uniformed (e.g. patent document 2).
A technology is disclosed where, in the sustain period, the switch timing from the electric power recovering circuit to a clamping circuit of a sustain pulse that belongs to a first group including the firstly applied sustain pulse is delayed comparing with sustain pulses that belong to the other groups, thereby suppressing the variation in light emission intensity in each discharge cell to improve the display quality (e.g. patent document 3).
Recently, the screen size and luminance of the panel have been increased, and hence power consumption of the panel is apt to increase. Recent increase in definition of the panel increases the number of electrodes to be driven, and hence further increases the power consumption. Therefore, the power consumption is desired to be further reduced.
Regarding a panel whose screen size and definition are increased, the load during driving of the panel increases, so that the discharge is apt to become unstable and hence it is further important to cause stable sustain discharge.
In the technology disclosed in patent document 2, for example, a sustain pulse having steep rising can suppress variation in light emission intensity in each discharge cell and cause stable sustain discharge. However, the recovery efficiency in the electric power recovering circuit decreases, and hence it is difficult to reduce the power consumption.
In the technology disclosed in patent document 3, a sustain pulse whose rising is moderated by delaying the switch timing from the electric power recovering circuit to the clamping circuit comparing with the sustain pulses that belong to the other groups can produce the following effects:                suppressing variation in light emission intensity in each discharge cell, and        increasing the recovery efficiency in the electric power recovering circuit to reduce the power consumption.        
However, the sustain pulse whose rising is moderated has a discharge intensity lower that that of the sustain pulse whose rising is steep, and hardly produces sufficient wall charge in the discharge cell. In the technology disclosed in patent document 3, disadvantageously, this sustain pulse continuously occurs and hence the sustain discharge hardly occurs.    [Patent document 1] Japanese Translation of PCT Publication No. H07-109542    [Patent document 2] Japanese Patent Unexamined Publication No. 2005-338120    [Patent document 3] Japanese Patent Unexamined Publication No. 2006-146035